What's the process of a supernova?

What is the process of a supernova ? Are any nearyb stars candidates ? Are we likesly to witness any in our galexy in our lifetime, and will we survive a neirby supernova?

Well first of all a star dies and explodes.This can be triggered by the turning off or turning on of nuclear fusion.The explosion is extremely bright.ANd I mean it can light up thw whole galaxy.When that star explodes it releases radiation and I mean A LOT of radiation.The same type of energy the sun releases in billions of years.This explosion shoots out most of the stars own material.Then it drives a shock wave through its surroundings.Then a structure,the result of a supernova and bounded by the expanding shockwave,is created.
Generally a supernova occurs once every 50 years in a galaxy the size of ours.In our own galaxy,the milky way galaxy,the star candidates would be the Rho Cassiopeiae,Spica,Betelgeuse,Eta Carinae,etc.The nearest supernova candidate to earth is the IK pegasi.It is about 150 light years from our planet.
I am not sure we are likely to witness it in our life time.I mean I know it happens about once every 50 years in a galaxy but there are billions of other galaxies that exists.I mean in 1885 there was a supernova in the Andromeda Galaxy.It is about 2.5 million light years away.It is the nearest spiral galaxy to our own.
A supernova will have to be less than 100 light years away to have an impact to our biosphere.It will release gamma rays,which can start a chemical reaction in the atmosphere.Causing nitrogen to turn into nitrogen oxides.It will depelte the ozone layer and admit harmful solar and cosmic radiation.Our planet has known five major extinction events.A nearby supernova was proposed to be the second cause of the the five major extinction events.It killed 60% of the oceanic life on earth.I think the answer to whether we survive or not a nearby supernova depends on how close it is.But the fact is it will cause a lot of harm if it is too close that's for sure.